This invention relates to the art of gas burning torches and more particularly to an improved fuel gas and oxygen mixer for a cutting torch.
Fuel gas-oxygen cutting torches are of course well known and generally comprise a torch head having outlet passages communicating with a torch tip or nozzle through which a combustible gaseous mixture flows and is ignited and directed toward a workpiece. The torch further includes fuel gas and oxygen supply lines connected to corresponding sources of fuel gas and oxygen, and valves for controlling the flow of fuel gas and oxygen to the torch head. Such torches have preheat and cutting modes of operation. In the preheat mode, the fuel gas and oxygen are combined in a mixer to provide a combustible mixture which flows to a torch head outlet and nozzle and which mixture is ignited to form a preheat flame which is used to heat a workpiece to a temperature which will support combustion. In the cutting mode, cutting oxygen is supplied to the torch head and nozzle separate from the preheat combustible mixture to flow from the nozzle to cut the heated workpiece.
It will of course be appreciated that the function of the fuel gas-oxygen mixer is to mix the fuel gas and oxygen components separately supplied thereto and to deliver the mixture to the torch head outlet and tip. Further, the mixer must supply a uniform mixture of fuel gas and oxygen to the point of combustion in order to achieve uniform combustion efficiency throughout the flame resulting from igniting the combustible mixture, and the fuel gas and oxygen flow rates to and through the mixer must be adequate for the required flow rates for a given torch at the available fuel gas and oxygen supply pressures. A further performance requirement with regard to the fuel gas-oxygen mixer is resistance to flashback. In this respect, it is commonplace during use of such a torch for a backfire to occur if, for example, the torch tip contacts the workpiece causing an explosion inside the torch between the point of mixing of the fuel gas and oxygen and the point of combustion at the torch tip. If such backfiring results in sustained combustion inside the torch the latter condition is defined as flashback, and flashback can quickly destroy a torch. Accordingly, the fuel gas-oxygen mixer must be capable of handling a considerable number of backfires in rapid succession without the occurrence of flashback.
When a backfire occurs, some of the exploded gases exit in the normal direction of flow through the torch tip and the remainder of the gases exit in the reverse direction through the fuel gas and oxygen inlet passages to the mixer. In order to avoid flashback when the reverse flow stops and the fuel gas and oxygen re-enter the mixer through the inlet passages, the area between the point of mixing in the mixer and the flame holes at the torch tip must either be free of a combustible mixture or free of a source of ignition. The latter conditions are influenced in part by factors directly related with the torch tip, torch and inlet gas pressures and in part by factors directly related to the mixer structure. With regard in particular to the latter, these factors include the area of the oxygen inlet passage or passages into the mixer, the cross-sectional, length and volume dimensions of the passage in which the gases are mixed, and the ability to achieve cooling with respect to the mixer during normal operation and quenching with respect to the reverse flow of hot gases through the mixer during backfire. Mixer designs heretofore available are limited with respect to the length of the mixer and mixing passage as well as the configuration of the gas flow paths thereto and therethrough, whereby protection against flashback is less than desirable.